1. Field of the Invention
This invention relates to a trim press for severing articles from a sheet of thermoplastic material in which articles have been differentially pressure formed and more particularly to a trim press including new and novel variable speed ejector mechanism for initially slowly ejecting a severed article from the sheet, increasing the ejection velocity as the ejector mechanism moves the severed article to its fully downstream ejecting position, and then even more rapidly retracting the ejector mechanism to its starting position.
2. Description of the Prior Art and Objects
Apparatus, such as that disclosed in U.S. Pat. No. 3,664,791, granted to G. W. Brown on May 23, 1972, which is incorporated herein by reference, has been provided heretofore for successively delivering a heated thermoplastic sheet to a sheet heating station, then to a forming station at which opposed die parts engage the sheet to differentially pressure form three dimentional articles in the sheet, and then to a trim station at which articles are severed from the sheet.
U.S. Pat. No. 4,313,358, granted to Gaylord W. Brown on Feb. 2, 1982, which is incorporated herein by reference, discloses a reciprocally movable trim die assembly including hollow cylindrical die knives and an opposed reciprocally moving trim die having trim punches which move between remote positions in which the sheet is indexed to the trim station and sheet trimming positions, engaging opposite sides of the sheet, to trim articles positioned at the trim station. The latter mentioned patent discloses article ejectors mounted in hollow die punches for movement relative thereto between retracted positions received by the hollow die punches, when the die assemblies are in the spaced apart positions, and advanced, ejecting positions projecting from the hollow punches after the articles are severed from the sheet.
The ejectors disclosed in the latter mentioned patent are driven via a cam and cam follower assembly which essentially "hammers" the ejector to the projected, ejecting position. Such "hammering" causes substantial loading, which can have a dilatorious effect on the machine bearings.
High speed ejection with a very high speed ejector which "hammers" the part, can crush the part upon impact. Such "hammering" can sometimes propel the part far beyond that which would normally be desired. It has been found advantageous to initially contact the part with a slowly moving ejector, and then increasing the velocity as the part is moved downstream. Accordingly, it is an object of the present invention to provide new and novel apparatus for trimming and ejecting parts integrally thermoformed in a sheet of thermoplastic material from the sheet which will rapidly eject a part without damaging the part.
It is another object of the present invention to provide a new and novel apparatus for trimming and ejecting articles integrally thermoformed in a sheet of thermoplastic material from the sheet which will start the ejection at a relatively low velocity, increase the velocity as it moves downstream and then even more rapidly retract the ejector to increase production.
U.S. Pat. No. 4,391,171, granted to Michael Wendt on Jul. 5, 1983, discloses a trim press including an ejector which is mounted on the trim die propelling apparatus for movement therewith and relative thereto. The article ejector in the latter mentioned patent is mounted on the moving die assembly for movement therewith and mechanism is provided for moving the article ejector relative to the moving trim die including a set of levers and associated eccentric cams which are actuated in timed relation.
Some of the prior art trim presses have incorporated cam boxes for controlling the movement of the ejector rods relative to the trim platen. There is a limitation on the operational speed of a system employing cam boxes which are relatively complicated and relatively difficult to be understood by users in the field.
Accordingly, it is a further object of the present invention to provide method and apparatus for actuating part ejector rods which will be more readily and easily understood, operated and repaired by users.
Another problem typically faced with the prior art trim presses having part ejectors is the loss of production time which occurs while the part ejector is positioned in the path of the sheet. Accordingly, it is another object of the present invention to provide new and novel apparatus for trimming and ejecting parts integrally thermoformed in a sheet of thermoplastic material from the sheet which will decrease the length of time a part ejector is disposed in the path of a sheet during the ejecting process.
It is another object of the present invention to provide trimming and ejecting apparatus of the type described which includes toggle linkage mechanism for moving the ejectors.
It is yet another object of the present invention to provide trimming and ejecting apparatus of the type described including ejector rods movable in a to-and-fro path of travel and mechanism for moving the ejector rods including first and second toggle links swingably coupled to each other to at least one trim die about a plurality of axes and movable between opposite sides of a plane intersecting the axes.
A still further object of the present invention is to provide new and novel trimming and ejecting apparatus and method of the type described which includes toggle links and mechanism for yieldably urging the ejectors to a retracted position but allowing forward movement thereof.
A still further object of the present invention is to provide trimming and ejecting apparatus and method of the type described including mechanism for moving the ejectors from a rest position to an ejecting position and return in response to relative movement of the trim dies away from each other and wherein the ejectors remain stationary as the trim dies are oppositely moved to a closed position.
It is another object of the present invention to provide a trimming and ejecting apparatus of the type described which will provide more time to feed the sheet and thus allow a system to operate on a shorter stroke.
It is a further object of the present invention to provide apparatus of the type described which will minimize the wear of the movable machine parts.
Other objects and advantages of the present invention will become apparent to those of ordinary skill in the art as the description thereof proceeds.